Jan Soulsby said the emotional burden and weight of responsibility for a surviving parent was enormous. “Why is this government adding further pressure by taking away a small amount of financial support?” she said.

Soulsby was among the group of widowed parents protesting in Westminster after a change in the rules dramatically reduced the amount paid out after a death.

Changes to the widowed parents’ allowance mean a benefit of about £112 a week until the youngest child leaves full-time education, which could be 20 years, has been replaced by £350 a month (£80 a week) for a maximum period of just a year and a half.

One terminally ill man gave an interview to the Guardian in the days before the ruling was changed, in which he said his survival beyond the deadline of 6 April would take over £50,000 from his wife and children.

“My death, on or before Thursday, changes my family’s wellbeing to the tune of tens of thousands. It is utterly unbelievable,” he said.

“In every classroom in the UK, one child will have lost their mum or dad; 780 parents die a week in the UK. Grief is an ongoing process – it doesn’t stop at 18 months, as Prince Harry says. Even after 20 years since his mother’s death, he is only now coming to terms with the pain and trauma of his grief,” said Magistris whose husband, Graham, died in September 2014 from a rare cancer.

Other protesters cited the example of footballer Rio Ferdinand, who lost his wife to breast cancer and has spoken out about the challenge of raising their three children without her.

Among those at the event were Erica Clarke, whose husband of 24 years died in 2005 from a heart attack, and Nansi Eggleton, who said: “We are asking the government to reconsider these changes now, before their impact is felt. The evidence shows that 75% of widowed parents will be worse off as a result of these changes, many receiving tens of thousands of pounds less than under the old system.

“Eighteen months just isn’t long enough for a family to recover from the loss of a parent. In fact in my case it was probably the most difficult time of all. Losing financial support at that stage would have been a disaster for me, and will be for many families, if these cuts aren’t turned around.”

Another woman, who gave her name as Mia, agreed, saying: “Grief doesn’t have a time limit.”

A government spokesperson has defended the policy: “We’re modernising the support we offer, replacing an outdated system that doesn’t reflect people’s lives today. The new bereavement support payment is simpler, easier to understand, tax-free and doesn’t affect the amount received from other benefits, so families can access wider welfare support.”

Sources in Downing Street said the change had been put in place by the coalition government.